Numerous different aerosol formulations are known, and there are numerous applications for the spraying or dispensing of an ingredient with a propellant. Because there are environmental concerns associated with many common propellants, there is a continued need to develop alternative propellant systems.
Carbon dioxide has been used as an aerosol propellant for many years (see, e.g., U.S. Pat. No. 2,524,590 to Boe), but was, in general, replaced by the current generation of propellants.
U.S. Pat. No. 5,169,433 to Lindsay et al. describes methods of preparing mixtures of active ingredients and excipients using liquid carbon dioxide, but requires the suspended material to be substantially soluble in the carbon dioxide.
U.S. Pat. No. 5,301,664 and U.S. Pat. No. 4,970,093, both to Sievers, concern methods of generating aerosols with a carbon dioxide propellant, but the carbon dioxide is used in a supercritical state. Supercritical carbon dioxide requires high-pressure containment.
U.S. Pat. No. 4,161,458 concerns the formulation of water-based aerosols using carbon dioxide as a propellant.
U.S. Pat. No. 4,139,607 to Simons describes the use of mixed propellant systems in which fluorinated dimethyl ethers are employed in liquid form and carbon dioxide is employed in gaseous form.
Means for delivering particulate matter (i.e., solid particles) with a liquid carbon dioxide propellant have neither been suggested nor described.